Effects of temperature on the activity of the p-nitrosubstituted diphenyl ether herbicide acifluorfen in cucumber ( Cucumis sativus L.)

Abstract

The influence of temperature on the activity of the herbicide acifluorfen (AF) (2-chloro-4-(trifluoromethyl)phenoxy-2-nitrobenzoate) in cucumber cotyledon disks exposed to light after being loaded with AF in darkness was small; generally > 90% of the 30°C effect at 3°C. The effects of 0.3 to 30 μ M acifluorfen on rapid (5 hr) disruption of the plasmalemma and slower (24 hr) photobleaching of chlorophyll were approximately the same at 3 and 30°C. In similar experiments, the herbicidal activity of rose bengal, a photodynamic dye, was also little affected by temperature. The activity of paraquat, however, was reduced by ca. 75% at 3°C compared to 30°C. Pretreatment with antimycin A during the dark incubation reduced the herbicidal activity of both AF and rose bengal equally well at both 3 and 30°C. Experiments with radiolabeled AF showed that the effect of antimycin A was not on AF uptake during the dark loading period prior to light exposure, suggesting that antimycin A acts as a radical scavanger or that mitochondrial respiration is a requirement for a process that potentiates sensitivity to photodynamic damage. Photosystem II inhibitors (atrazine and DCMU) enhanced the activity of AF at 30°C, but had no effect at 3°C, suggesting that a functional photosynthetic system provides some level of protection from AF by regeneration of antioxidants. These data indicate that there is no metabolic requirement for AF activity after it arrives at its site of action and is associated with its chromophore.